Multi-Reference Switching Amplifiers, of the type shown in U.S. Pat. No. 6,535,058 and PCT/US99/26691, the content of these being incorporated herein by reference, yield significantly higher instantaneous resolution than standard switching amplifiers, through the summation of multiple modulated outputs. In that they operate with pulsewidth modulated (PWM) signals, however, multi-reference amplifiers (like all Class D amplifiers) are subject to distortion unless phase correction is applied.
Switching amplifiers usually rely upon modulation of pulsewidths controlling switching devices which gate power to the load. Resultant output power then approximates the integral of the gated voltage or current over the output sampling period. As these pulsewidths change with dynamic data, however, pulsewidth position within the output sample period becomes significant. Considerable distortion is induced unless the relative phase of each output pulse remains constant. Centering output pulses in the output sample period typically ensures instantaneous phase coherency. It is for this reason that many analog switching amplifiers use triangle, as opposed to sawtooth, reference waveforms.
Multi-reference amplifiers, which sum and/or time-multiplex several switched references, require coherent relative phase of all switched reference pulsewidths to ensure low distortion. Additionally, pulsewidths unrelated to modulation values are typically added to each of these switched reference pulsewidths, as illustrated in my U.S. Pat. No. 6,492,868 “Dynamic Range Enhancement Technique,” the entire content of which is also incorporated herein by reference. To ensure coherent relative phase of this plurality of pulsewidths can be a difficult task. A need therefore exists for an effective method of correcting instantaneous phase errors in multi-reference switching amplifiers.